180 MICRO-ORGANISMS AND FERMENTATION. 



(A) He found in the case of the typical Saceharomyces 

 species, that when their cells were cultivated in aerated wort at 

 a temperature above the maximum for their spore-formation and 

 near the maximum for their vegetative growth, they were affected 

 in such a manner that they lost their power of forming spores 

 and films, and the same applies also to the innumerable genera- 

 tions successively formed in new cultures under the most 

 varied conditions. He succeeded also in bringing about such a 

 transformation by cultivation on solid media. 



In some of the species treated in this way, it was also 

 observed that, in wort-cultures, they yielded a more abundant 

 crop of yeast, but a slower fermentation. This was, for 

 instance, the case with Carlsberg low-fermentation yeast No. 2. 

 The newly formed variety attenuated more slowly and weakly 

 than the original species ; but at the same time the clarifica- 

 tion was better. 



KAYMAN and KRUIS have shown that the cells present in 

 films possess the power of oxidising alcohol produced during 

 the fermentation, into carbon dioxide and water. HANSEN'S 

 varieties, while completely losing the power of forming films, 

 are rendered incapable of performing this oxidising action. 

 Thus, while a flask, containing the original species, which had 

 developed a luxuriant film after six months' standing, showed 

 only 1*5 per cent, by volume of alcohol, a parallel flask, 

 which showed no film-formation, contained 5 '5 per cent, of 

 alcohol a quantity equal to that found at the end of the 

 first month. 



In another series of experiments HANSEN showed that the 

 action of higher temperatures upon the cells without aeration 

 was capable of producing radical and lasting alterations of a 

 different kind in the nature of the plasma. When Carlsberg 

 low-fermentation yeast No. 1. was cultivated in wort at 32 C\ 

 through eight cultures, each successive culture being inocu- 

 lated from the preceding one, which had been left undisturbed 

 until the end of the fermentation, a variety was evolved in the 

 ninth culture which, in wort of 14 Balling, to which 10 per 

 cent, of saccharose had been added, formed 1-2 per cent, by 

 volume less alcohol than the original form. The new variety 

 clarified better under brewery conditions, and gave a weaker 



